POS0906 PREVALENCE OF SPECIFIC AND ASSOCIATED MYOSITIS ANTIBODIES IN A COHORT OF PNEUMOLOGICAL PATIENTS: FROM THE DIAGNOSIS OF INTERSTITIAL LUNG DISEASE TO A POSSIBLE DIAGNOSIS OF CONNECTIVE TISSUE DISEASE
Authors: F. Angeli, E. Pedretti, M. Fredi, I. Cavazzana, D. Modina, P. Ceruti, L. Andreoli, E. Garrafa, F. Franceschini
Journal: Annals of the Rheumatic Diseases (2022)

Background Interstitial lung disease (ILD) could be the first and only manifestation of idiopathic inflammatory myopathies (IIMs). Myositis-associated (MAA) or myositis-specific autoantibodies (MSA) are found in 60%-65% of cases [1, 2], but only anti-Jo1 have been included in EULAR 2017 criteria [3]. Objectives Aim of this work is to evaluate the presence of MSA/MAA in patients with ILD on serum analyzed by line blot (LB) immunoassay, the associated clinical diagnoses and the consistency of these diagnoses with antibody specificity. Methods Between march 2017 and march 2021, 267 sera were analyzed for MSA/MAA, 84 (31.4%) of which requested after a pneumological evaluation. The search was performed by LB (EUROLINE, Autoimmune Inflammatory Myopathies 16 Ag Profile). Medical records were analyzed for patients with at least one MSA/MAA and diagnosis divided in: connective tissue disease (CTD), interstitial pneumonia with autoimmune features (IPAF) or only pneumological diagnosis. Results A positivity for at least one MSA/MAA was found in 37/84 (44%) patients that had the following pneumological diagnosis: 13 non-specific interstitial pneumonia (NSIP, 35.1%), 10 organizing pneumonia (OP, 27%), 10 usual interstitial pneumonia (UIP, 27%), 1 acute interstitial pneumonia (AIP, 2.7%), 1 lymphoid interstitial pneumonia (LIP, 2.7%), 1 iatrogenic ILD for amiodarone (2.7%) and 1 idiopathic pulmonary artery hypertension (IPAH, 2.7%). Distribution of antibodies is reported in Table 1. The most frequent autoantibody was anti-Ro52 (13 sera, 35.2%), while anti-Mi2 was the most frequent MSA (10 sera, 32.4%) followed by anti-Jo1 and anti-SRP with 5 (13.5%) positive sera each. In Figure 1 the heat-map represents the frequency of MSA/MAA and their mutual associations. Multiple autoantibodies were found in 17 (46%) sera. More than one MSA was found in 8 (21.6%) sera of patients with the following diagnosis: 4 only pneumological diseases, 3 ASS and 1 IPAF. Table 1. Distribution of MSA/MAA and associated autoimmune diseases Autoantibodies distribution N (%) Sera with a single MSA/MAA (N/positive; %) CTD* (N/positive; %) IPAF (N/positive; %) MSA Jo-1 = 5 (13.5) 2/5 (40) 3/5 (60) 0 PL7 = 4 (10.8) 0 2/4 (50) 1/4 (25) PL12 = 6 (16.2) 3/6 (50) 3/6 (50) 0 OJ = 3 (8.1) 2/3 (66.6) 1/3 (33.3) 2/3 (66.6) EJ = 1 (2.7) 1/1 (100) 1/1 (100) 0 Mi-2 = 10 (32.4) 3/10 (30) 2/10 (20) 0 NXP2 = 1 (2.7) 0 0 1/1 (100) SRP = 5 (13.5) 2/5 (40) 2/5 (40) 0 TIF1gamma = 2 (5.4) 0 1/2 (50) 0 MAA Ro-52 = 13 (35.2) 3/13 (23) 9/13 (69.2) 1/13 (7.6) PM/Scl = 6 (18.9) 4/6 (66.6) 0 1/6 (16.6) For some patients there are multiple positive antibodies. *The following diagnosis were included: antisynthetase syndrome, dermatomyositis, polymyositis and systemic sclerosis. During the diagnostic work-up, at least one MSA/MAA were detected in 13 patients diagnosed with a CTD (35%), 5 with a IPAF (13%), 19 (51%) only a pneumological diagnosis. Of these 19 patients, 11 (57.9%) had a single autoantibody positivity (8 for a MSA, 3 for a MAA) while 8 (42.1%) had multiple positivity (4 with a MSA plus MAA and 4 with multiple MSA positivity). The most frequently diagnosed CTD was ASS with 9 patients (24.3%), followed by 2 polymyositis (5.4%), 1 dermatomyositis (2.7%) and 1 systemic sclerosis (2.7%). Pulmonary involvement in patients with CTD was represented by 9 cases of NSIP (69,3%) and 4 UIP (30,7%). Conclusion During the last 4 years about 1/3 of research for MSA/MAA requests to our laboratory had a pneumological indication and MSA/MAA were found in 44% of these patients. In patients with pulmonary involvement and MSA/MAA positivity 35% developed a CTD. Interstitial lung disease could be the first manifestation of a systemic autoimmune disease: research for MSA/MAA and a collaboration between rheumatologist and pneumologist allows a correct diagnostic work-up and therapeutic approach. References [1]Betteridge Z, et al. J Autoimmun 2019;101:48-55 [2]Vojinovic T, et al. Clin Rev Allergy Immunol. 2021 Feb;60(1):87-94 [3]Lundberg IE, et al. Ann Rheum Dis 2107;76:1955-1964 Disclosure of Interests None declared